The present invention relates to quick-drying coating compositions, and preferably to coating compositions for application to natural or artificial fingernails or toenails under ambient conditions.
Numerous types of coating compositions, and particularly liquid nail coating formulations, are sold commercially. Liquid nail coating formulations typically contain a primary film former such as nitrocellulose, a secondary film former such as toluene-sulfonamide-formaldehyde resin, a plasticizer such as camphor or dibutyl phthalate, and one or more solvents such as toluene (toluol), lower aliphatic alcohols, and acetates. In addition, these formulations usually contain coloring agents and fragrances.
There are a number of desirable properties which nail coating compositions such as nail polish should possess. In particular, a nail polish should dry and harden quickly, apply easily, be adherent, glossy, waterproof and suitably colored, wear well, be elastic, resist chipping, peeling and abrasion for a reasonable period of time, and be dermatologically innocuous. In addition, nail polish formulations should exhibit good shelf stability and resist separation or settling out of their components, e.g., pigment components.
An important property of a nail coating such as a nail polish is its ability to dry rapidly when applied to a natural human, or even in some instances, natural animal (such as dogs) or artificial fingernail or toe nail. In practice, this rapid-drying property is difficult to achieve while retaining the other desirable characteristics such as gloss, wear resistance, etc. The coating process, however, can be time consuming since a coating of polish must dry before a subsequent coating can be applied to the first coating. Since the average drying time for a coating of conventional nail polish is about five minutes, the total time for completing the nail polishing process using conventional coating compositions can be 15 minutes or more.
The time consuming aspects of applying nail polish is of particular concern to women who work outside the home. These women need to have a product which can be easily applied and which dries in the shortest amount of time. Also, in the manicure and pedicure industries such as nail care and beauty salons, a nail polish which can dry in a period less than about one minute would provide a significant advantage over the prior art compositions.
The art has attempted to reduce the time required for drying of nail polishes. Such prior art nail coating compositions generally use solvent systems that are relatively volatile under ambient conditions. The term "under ambient conditions" as used herein refers to ambient temperature and humidity conditions typical of indoor environments, i.e., about 15.degree. C. to 25.degree. C. (about 59.degree. F. to about 77.degree. F.) and about 20% to 70% relative humidity.
A preferred volatile solvent in prior art nail coating composition is acetone, but acetone has several drawbacks when used in nail coating formulations. Besides being highly flammable, acetone in nail coating formulations causes bottleneck fouling in nail polish bottles with repeated use and causes difficulty in coating leveling when applied with a nail polish brush. Acetone is a hygroscopic solvent, so water contamination from atmospheric moisture often renders the polish unusable after the nail polish bottle has been opened for use several times. An additional drawback is that severe pigment discoloration is observed with acetone-containing nail polish formulations that are exposed to elevated temperature above ambient conditions.
Other components present in prior art nail coating compositions are known environmental or health hazards, being chemicals that are detrimental to air quality or are suspected human carcinogens or are toxic to humans. For example, prior art nail coating compositions that rely on volatile solvents such as acetone to obtain rapid drying once the composition is applied to nails result in undesirable volatile organic carbon (VOC) emissions that contribute to air pollution.
Toluene, a component that allows nail coating lacquers to dry to high gloss films with good fingernail-adhesion properties, is moderately toxic through skin absorption or inhalation and is an embryofetatoxin. Chlorinated hydrocarbon solvents, such as methylene chloride, trichlorethane, methyl chloroform and the like, often used in nail coating formulations to reduce drying time and increase compatibility of other components in the formulation, are cancer suspect agents and are known to be detrimental to the environment, particularly to the ozone layer. Formaldehyde-containing resins are used in some prior art nail polish formulations to impart flexibility and good fingernail-adhesion properties but are undesirable due to the presence of formaldehyde, a suspected human carcinogen. Other known solvent systems contain acetone, which is added to standard nail polish formulations to substantially hasten drying of a nail enamel composition to a durable, hard finish, but acetone is a highly volatile and noxious solvent.
A need therefore continues for coating formulations, especially nail coating formulations, which can dry rapidly and which overcome the disadvantages of the art, by omitting detrimental or undesirable components such as those described above.